Heat-sensitive recording medium

Abstract

Disclosed is a heat-sensitive recording medium having, on a support, a heat-sensitive recording layer containing at least a leuco dye, a developer, and a sensitizer, the heat-sensitive recording medium being characterized in that the heat-sensitive recording layer contains, as developers, 1,3-diphenylurea and 5-(N-3-methylphenyl-sulfonamido)-(N',N''-bis-(3-methylphenyl)-isophthalic acid diamide.

Description

Thermal recording device

[0001] This invention relates to a thermal recording material.

[0002] Thermal recording media that record colored images using the heating-induced color reaction between colorless or light-colored leuco dyes and phenols or organic acids are widely used. Because such thermal recording media form colored images simply by heating, they offer advantages such as compact recording devices, easy maintenance, and low noise generation. Therefore, thermal recording media are widely used as information recording materials in various applications, including label printers, automatic ticket vending machines, CD / ATM machines, order slip output machines in restaurants, and data output machines for scientific research equipment.

[0003] Because the color reaction is reversible, it is known that the colored image fades over time. This fading reaction is accelerated in high-temperature, high-humidity environments and further accelerated by contact with oils, plasticizers, etc., which can cause the recorded image to fade to the point of being unreadable. In particular, contact with water is an event that can occur in all applications of thermal recording materials, and the ability of the colored image to not fade in such environments has long been cited as a requirement for improving the performance of thermal recording materials.

[0004] Generally, color-developing compounds containing phenolic hydroxyl groups exhibit high color-developing ability. Among these, bisphenol compounds have been reported in numerous studies due to their high color intensity, with 2,2-bis(4-hydroxyphenylpropane) (bisphenol A) and 4,4'-dihydroxydiphenylsulfone (bisphenol S) being proposed. However, these compounds have the drawback of poor water resistance in the printed area. Furthermore, the use of phenol compounds such as bisphenol A is being questioned due to endocrine problems. Therefore, there is a demand for non-phenol color developers that do not contain a phenolic structure.

[0005] In response to such demands, thermal recording materials containing non-phenolic color developers such as 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, N-[2-(3-phenylureido)phenyl]benzenesulfonamide, N-(p-toluenesulfonyl)-N'-3-p-toluenesulfonyloxyphenyl)urea, and 1,3-diphenylurea (DPU) have been proposed (Patent Documents 1 and 2). However, many of these have room for improvement in achieving both color development performance and water resistance.

[0006] Patent No. 7286053 Patent No. 7286054

[0007] The main objective of this invention is to provide a thermal recording medium that contains a non-phenolic compound as a color developer, is highly sensitive, has excellent intermediate printing density, and is highly water-resistant.

[0008] In view of the above-mentioned prior art, the present inventors have conducted extensive research and have succeeded in solving the above-mentioned problems. That is, the present invention relates to the following thermal recording body.

[0009] Item 1: A thermal recording body having a thermal recording layer on a support containing at least a leuco dye, a color developer, and a sensitizer, characterized in that the thermal recording layer contains 1,3-diphenylurea and 5-(N-3-methylphenyl-sulfonamide)-(N',N''-bis-(3-methylphenyl)-isophthalic acid diamide as color developers. Item 2: The thermal recording body according to Item 1, wherein the thermal recording layer further contains at least one color developer selected from the group consisting of N-[2-(3-phenylureido)phenyl]benzenesulfonamide, 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, N,N'-di[3-(p-toluenesulfonyloxy)phenyl]urea, and diaminodiphenylsulfone. Item 3: A thermal recording body according to item 1 or 2, wherein 5-(N-3-methylphenyl-sulfonylamide)-(N',N''-bis-(3-methylphenyl)-isophthalic acid diamide) is contained in an amount of 5 to 300 parts by mass per 100 parts by mass of 1,3-diphenylurea. Item 4: A thermal recording body according to item 2 or 3, wherein N-[2-(3-phenylureido)phenyl]benzenesulfonamide is contained in an amount of 10 to 300 parts by mass per 100 parts by mass of 1,3-diphenylurea. Item 5: A thermal recording body according to any one of items 1 to 4, wherein the thermal recording layer contains at least one selected from the group consisting of diphenylsulfone, 1,2-diphenoxyethane, and 1,2-di(3-methylphenoxy)ethane as a sensitizer. Item 6. A thermal recording body according to any one of items 1 to 5, comprising a primer layer between the support and the thermal recording layer, wherein the primer layer contains hollow particles and an adhesive, the hollow particles having a maximum particle diameter (D100) of 10 to 30 μm, a particle diameter (D50) at a 50% volume frequency of the hollow particles of 4.0 to 15 μm, a ratio D100 / D50 of the maximum particle diameter (D100) to the particle diameter (D50) at a 50% volume frequency of the hollow particles of 1.8 to 3.0, and a volume percentage of hollow particles with a particle diameter of 2.0 μm or less of 1% or less.

[0010] The thermal recording material of the present invention contains a non-phenolic compound as a color developer, and exhibits high sensitivity, excellent intermediate printing density, and excellent water resistance.

[0011] In this specification, the expression "includes" includes the concepts of "includes," "substantially consist of," and "consisting only of." In this specification, numerical ranges expressed using "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits. In the present invention, latex includes the state of a gel or dried film formed by drying a dispersion medium.

[0012] The present invention relates to a thermal recording body having a thermal recording layer on a support containing at least a leuco dye, a color developer, and a sensitizer, characterized in that the thermal recording layer contains 1,3-diphenylurea and 5-(N-3-methylphenyl-sulfonamide)-(N',N''-bis-(3-methylphenyl)-isophthalic acid diamide as color developers.

[0013] [Support] The support in this invention is not particularly limited in terms of type, shape, dimensions, etc. For example, it can be appropriately selected and used from among high-quality paper (acidic paper, neutral paper), medium-quality paper, coated paper, art paper, cast-coated paper, glassine paper, resin-laminated paper, polyolefin-based synthetic paper, synthetic fiber paper, nonwoven fabric, cellophane, synthetic resin film, and various transparent supports. Examples of resins in resin-laminated paper and synthetic resin films include polyester resins such as polyethylene terephthalate (PET), polyolefin resins such as polypropylene (PP) and polyethylene (PE). When glassine paper is used as the support, an anchor coat layer containing polyethyleneimine is provided on the glassine paper, and a resin layer mainly containing polypropylene with a small amount of polyethylene is provided on the anchor coat layer by melt extrusion lamination as a first resin layer, thereby increasing the interlayer strength between the glassine paper and the first resin layer. Alternatively, a second resin layer containing polyethylene can be provided between the anchor coat layer and the first resin layer by melt extrusion lamination. The thickness of the support is not particularly limited, and is usually around 5 to 200 μm. The density of the support is also not particularly limited, and is typically 0.60 to 2.00 g / cm³. ３ A certain degree is desirable.

[0014] [Thermal Recording Layer] (Leuco Dyes) The thermal recording layer in the thermal recording body of the present invention may contain various known colorless or light-colored leuco dyes. Specific examples of such leuco dyes are listed below.

[0015] Specific examples of leuco dyes include, for example, blue-colored dyes such as 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-methylphenyl)-3-(4-dimethylaminophenyl)-6-dimethylaminophthalide, fluorane, 3-(N-ethyl-N-p-tolyl)amino-7-N-methylanilinofluorane, 3-diethylamino-7-anilinofluorane, 3-diethylamino-7-dibenzylaminofluorane, and rhodamine B-anilinolactam. Green coloring dyes such as 3,6-bis(diethylamino)fluoran-γ-anilinolactam, 3-cyclohexylamino-6-chlorofluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-7-chlorofluoran, red coloring dyes such as 3-(N-ethyl-N-isoamyl)amino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3 -di(n-butyl)amino-6-methyl-7-anilinofluorane, 3-di(n-pentyl)amino-6-methyl-7-anilinofluorane, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluorane, 3-diethylamino-7-(m-trifluoromethylanilino)fluorane, 3-(N-isoamyl-N-ethylamino)-7-(o-chloroanilino)fluorane, 3-(N-ethyl-N-2-tetrahydrofurfurylamino)-6-methyl-7-anilinofluorane, 3-( N-n-hexyl-N-ethylamino)-6-methyl-7-anilinofluorane, 3-[N-(3-ethoxypropyl)-N-ethylamino]-6-methyl-7-anilinofluorane, 3-[N-(3-ethoxypropyl)-N-methylamino]-6-methyl-7-anilinofluorane, 3-diethylamino-7-(2-chloroanilino)fluorane, 3-di(n-butylamino)-7-(2-chloroanilino)fluorane, 4,4'-bis-dimethylaminobenzhydrinbenzylether, N-2,4,5-Trichlorophenylleucoauramine, 3-Diethylamino-7-butylaminofluorane, 3-Ethyl-tolylamino-6-methyl-7-anilinofluorane, 3-Cyclohexyl-methylamino-6-methyl-7-anilinofluorane, 3-Diethylamino-6-chloro-7-(β-ethoxyethyl)aminofluorane, 3-Diethylamino-6-chloro-7-(γ-chloropropyl)aminofluorane, 3-Diethylamino-6-methyl-7-anilinofluorane, 3-(N-I Soamyl-N-ethylamino)-6-methyl-7-anilinofluorane, 3-dibutylamino-7-chloroanilinofluorane, 3-diethylamino-7-(o-chlorophenylamino)fluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-(p-toluidino)fluorane, 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluorane, 3-diethylamino -6-chloro-7-anilinofluorane, 3-dimethylamino-6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 2,2-bis{4-[6'-(N-cyclohexyl-N-methylamino)-3'-methylspiro[phthalide-3,9'-xanthene]-2'-ylamino]phenyl}propane, 3-diethylamino-7-(3'-trifluoromethylphenyl)aminofluorane, etc. Chromochemical dyes, 3,3-bis[1-(4-methoxyphenyl)-1-(4-dimethylaminophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide, 3,3-bis[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide, 3-p-(p-dimethylaminoanilino)anilino-6-methyl-7-chlorofluoran, 3-p-(p-chloroanilino)anilino-6-methyl-7-chlorofluoran, 3,Examples include dyes with absorption wavelengths in the near-infrared region, such as 6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide. Of course, the examples are not limited to these, and two or more compounds can be used in combination as needed.

[0016] The content of such leuco dye is not particularly limited, but is preferably about 3 to 30% by mass, more preferably about 5 to 25% by mass, and even more preferably about 7 to 20% by mass, of the total solid content of the thermal recording layer. By setting it to 3% by mass or more, the color development ability can be enhanced and the recording density can be improved. By setting it to 30% by mass or less, the heat resistance can be improved.

[0017] (Color Developer) In this invention, the thermal recording layer contains 1,3-diphenylurea and 5-(N-3-methylphenyl-sulfonamide)-(N',N''-bis-(3-methylphenyl)-isophthalic acid diamide) as color developers, which are non-phenol color developers. This improves the recording density and intermediate printing density, and also improves the water resistance of the printed area.

[0018] Preferably, the non-phenol developer further contains at least one developer selected from the group consisting of N-[2-(3-phenylureido)phenyl]benzenesulfonamide, 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, N,N'-di[3-(p-toluenesulfonyloxy)phenyl]urea, and diaminodiphenylsulfone (e.g., 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone). This can further improve the recording density and intermediate printing density. Among these, N-[2-(3-phenylureido)phenyl]benzenesulfonamide is particularly preferred.

[0019] The content ratio of such color developer is not particularly limited, but is preferably about 0.1 to 40% by mass, more preferably about 10 to 35% by mass, and even more preferably about 15 to 30% by mass, of the total solid content of the thermal recording layer. By setting it to 0.1% by mass or more, the color development ability can be enhanced and the recording density can be improved. By setting it to 40% by mass or less, the heat resistance can be improved.

[0020] Furthermore, the content ratio of the color developer is generally preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, even more preferably 1 part by mass or more, even more preferably 1.2 parts by mass or more, and particularly preferably 1.4 parts by mass or more, per 1 part by mass of leuco dye. In addition, the content of the color developer is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 4 parts by mass or less, and particularly preferably 3.5 parts by mass or less, per 1 part by mass of leuco dye. Recording performance can be improved by using 0.5 parts by mass or more. On the other hand, background clouding in high-temperature environments can be effectively suppressed by using 10 parts by mass or less.

[0021] The content of 5-(N-3-methylphenyl-sulfonilamide)-(N',N''-bis-(3-methylphenyl)-isophthalic acid diamide) is preferably about 5 to 300 parts by mass, more preferably about 5 to 200 parts by mass, and even more preferably about 5 to 100 parts by mass, per 100 parts by mass of 1,3-diphenylurea. A content of 5 parts by mass or more can improve water resistance. A content of 300 parts by mass or less can improve color intensity.

[0022] When the thermal recording layer of the present invention contains N-[2-(3-phenylureido)phenyl]benzenesulfonamide as a non-phenol color developer, the content of N-[2-(3-phenylureido)phenyl]benzenesulfonamide is preferably about 10 to 300 parts by mass, more preferably about 30 to 250 parts by mass, and even more preferably about 50 to 200 parts by mass, per 100 parts by mass of 1,3-diphenylurea. The color development density can be improved by using 10 parts by mass or more. The water resistance can be improved by using 300 parts by mass or less.

[0023] Other color developers may be included as long as they do not impair the effects of the present invention. Specific examples of other color developers include, for example, 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4'-sec-butylidenediphenol, 4-phenylphenol, 4,4'-dihydroxydiphenylmethane, 4,4'-isopropylidenediphenol, 4,4'-cyclohexylidenediphenyl, 4,4'-cyclohexylidenediphenol, 1,1-bis(4-hydroxyphenyl)-ethane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, and 4,4'-bis (p-tolylsulfonylaminocarbonylamino)diphenylmethane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2'-bis[4-(4-hydroxyphenyl)phenoxy]diethyl ether, 4,4'-dihydroxydiphenyl sulfide, 4,4'-thiobis(3-methyl-6-tert-butylphenol), 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 2,4'-dihydroxydiphenyl Lufon, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-n-propoxydiphenyl sulfone, 4-hydroxy-4'-allyloxydiphenyl sulfone, 4-hydroxy-4'-benzyloxydiphenyl sulfone, 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone, bis(p-hydroxyphenyl)acetate butyl, bis(p-hydroxyphenyl)acetate methyl, hydroquinone monobenzyl ether, bis(3-allyl-4-hydroxyphenyl)sulfone, 4-hydroxy-4' -Methyldiphenylsulfone, 4-allyloxy-4'-hydroxydiphenylsulfone, 3,4-dihydroxyphenyl-4'-methylphenylsulfone, 4-hydroxybenzophenone, 4-dimethyl hydroxyphthalate, 4-methyl hydroxybenzoate, 4-propyl hydroxybenzoate, 4-sec-butyl hydroxybenzoate, 4-phenyl hydroxybenzoate, 4-benzyl hydroxybenzoate, 4-benzyl ester hydroxybenzoate, 4-tolyl hydroxybenzoate, 4-chlorophenyl hydroxybenzoate, 4,Phenolic compounds such as 4'-dihydroxydiphenyl ether, or benzoic acid, p-chlorobenzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, salicylic acid, 3-tert-butylsalicylic acid, 3-isopropylsalicylic acid, 3-benzylsalicylic acid, 3-(α-methylbenzyl)salicylic acid, 3,5-di-tert-butylsalicylic acid, 4-[2-(p-methoxyphenoxy)ethyloxy]salicylic acid Acids, aromatic carboxylic acids such as 4-[3-(p-tolylsulfonyl)propyloxy]salicylic acid, 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, and 4-[3-(p-tolylsulfonyl)propyloxy]zinc salicylate, and their phenolic compounds, salts of aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel, and further, thiocyanates. Organic acidic substances such as lead antipyrine complexes, complex zinc salts of terephthalaldehyde acid and other aromatic carboxylic acids, urea compounds such as N-p-toluenesulfonyl-N'-3-(p-toluenesulfonyloxy)phenylurea, N-p-toluenesulfonyl-N'-p-butoxycarbonylphenylurea, N-p-tolylsulfonyl-N'-phenylurea, 4,4'-bis(p-toluenesulfonylaminocarbonylamino)diphenylmethane, 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, thiourea compounds such as N,N'-di-m-chlorophenylthiourea, N-(p-toluenesulfonyl)carbamoyl acid p-cumylphenyl ester, N-(p-toluenesulfonyl)carbamoyl acid p-benzyloxyphenyl ester, N-(o-toluyl)-p-toluenesulfamide, etc., with -SO in the molecule. ２ Examples include organic compounds containing NH- bonds, activated clay, attapulgite, colloidal silica, and inorganic acidic substances such as aluminum silicate.

[0024] Furthermore, examples include urea urethane derivatives such as 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, 4,4'-bis[(2-methyl-5-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, and 4-(2-methyl-3-phenoxycarbonylaminophenyl)ureido-4'-(4-methyl-5-phenoxycarbonylaminophenyl)ureidodiphenylsulfone, represented by the general formula (1) below, and diphenyl sulfone derivatives represented by the general formula (2) below. Of course, the examples are not limited to these, and two or more compounds can be used in combination as needed.

[0025]

[0026] (In the formula, n represents an integer from 1 to 6.)

[0027] (Adhesive) The thermal recording layer in the present invention may contain an adhesive. As the adhesive, for example, either a water-soluble adhesive or a water-dispersible adhesive can be used. Examples of water-soluble adhesives include modified polyvinyl alcohol such as polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol; starch and its derivatives; cellulose derivatives such as methoxycellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, methylcellulose, and ethylcellulose; sodium polyacrylate; polyvinylpyrrolidone; polyamide; diisobutylene-maleic anhydride copolymer salt; styrene-acrylic acid copolymer salt; styrene-maleic anhydride copolymer salt; ethylene-maleic anhydride copolymer salt; acrylamide-acrylic acid ester copolymer; acrylamide-acrylic acid ester-methacrylic acid copolymer; polyacrylamide; sodium alginate; gelatin; casein; and gum arabic. Examples of water-dispersible adhesives include emulsions such as polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid esters, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, and ethylene-vinyl acetate copolymer, or latexes of water-insoluble polymers such as styrene-butadiene copolymer and styrene-butadiene-acrylic copolymer. Alternatively, an organic solvent-soluble adhesive can be used. Examples of organic solvent-soluble adhesives include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, polyurethane, saturated polyester, polyester polyurethane, epoxy resin, phenoxy resin, nitrocellulose, melamine resin, vinylpyrrolidone-vinyl acetate copolymer, chlorinated polyethylene, and chlorinated polypropylene. Vinylpyrrolidone-vinyl acetate copolymer is particularly preferred. The molar ratio of vinylpyrrolidone to vinyl acetate in such vinylpyrrolidone-vinyl acetate copolymer is not particularly limited, but 50 / 50 to 30 / 70 is preferred, and 40 / 60 to 30 / 70 is more preferred. By setting the ratio to 50 / 50 to 30 / 70, the print density can be improved.The adhesive can be used alone or in combination of two or more types. The content of the adhesive can be selected from a wide range, but generally it is preferably about 5 to 35% by mass, and more preferably about 9 to 33% by mass, of the total solid content of the thermal recording layer.

[0028] (Preservation Improvement Agent) In the present invention, the thermal recording layer may further contain a preservation improvement agent, mainly to further enhance the preservation of the color image. Examples of such preservation improvement agents include 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 1,1-bis(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 4,4'-[1,4-phenylenebis(1-methylethylidene)]bisphenol, and 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisphenol At least one compound selected from phenolic compounds such as 4-benzyloxyphenyl-4'-(2-methyl-2,3-epoxypropyloxy)phenylsulfone, 4-(2-methyl-1,2-epoxyethyl)diphenylsulfone, 4-(2-ethyl-1,2-epoxyethyl)diphenylsulfone, and isocyanuric acid compounds such as 1,3,5-tris(2,6-dimethylbenzyl-3-hydroxy-4-tert-butyl)isocyanuric acid can be used. Of course, it is not limited to these, and two or more compounds can be used in combination as needed.

[0029] When using a preservation improver, the amount used should be sufficient to improve preservation, and is usually preferably about 1 to 30% by mass, and more preferably about 5 to 20% by mass, of the total solid content of the thermal recording layer.

[0030] (Sensitizer) The thermal recording layer in the present invention contains a sensitizer. This makes it possible to increase the recording sensitivity. Examples of sensitizers include stearamide, methoxycarbonyl-N-stearate benzamide, N-benzoyl stearate, N-eicosanoamide, ethylenebisstearate, behenamide, methylenebisstearate, N-methylolstearate, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, diphenyl sulfone, p-benzyl oxybenzoate benzyl, 1-hydroxy-2-naphthoate phenyl, 2-naphthylbenzyl ether, m-terphenyl, p-benzylbiphenyl, di-p-chlorobenzyl oxalate, di-p-methylbenzyl oxalate, dibenzyl oxalate, p-trilbiphenyl ether, di(p-methoxyphenoxyethyl) ether, 1,2-di(3-methylphenoxy Examples include ethane, 1,2-di(4-methylphenoxy)ethane, 1,2-di(4-methoxyphenoxy)ethane, 1,2-di(4-chlorophenoxy)ethane, 1,2-diphenoxyethane, 1-(4-methoxyphenoxy)-2-(3-methylphenoxy)ethane, p-methylthiophenylbenzyl ether, 1,4-di(phenylthio)butane, p-acetoluidide, p-acetophenetidide, N-acetoacetyl-p-toluidine, 1,2-diphenoxymethylbenzene, di(β-biphenylethoxy)benzene, p-di(vinyloxyethoxy)benzene, 1-isopropylphenyl-2-phenylethane, di-o-chlorobenzyl adipate, 1,2-bis(3,4-dimethylphenyl)ethane, 1,3-bis(2-naphthoxy)propane, diphenyl, benzophenone, etc. Among these, at least one selected from the group consisting of diphenylsulfone, 1,2-diphenoxyethane, and 1,2-di(3-methylphenoxy)ethane is preferred. These can be used in combination to the extent that it does not cause any problems. The content of the sensitizer should be an amount that is effective for sensitization, and is usually preferably about 2 to 40% by mass, and more preferably about 5 to 25% by mass, of the total solid content of the thermal recording layer.

[0031] Other components that make up the thermal recording layer may include, if necessary, crosslinking agents, waxes, metal soaps, water-resistant agents, pigments, dispersants, colored dyes, fluorescent dyes, etc.

[0032] (Crosslinking agent) A crosslinking agent that hardens the adhesive of the thermal recording layer or other layers can be contained in the thermal recording layer. This can improve the water resistance of the thermal recording layer. Examples of crosslinking agents include aldehyde compounds such as glyoxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, melamine resins, glyoxylates, methylolurea compounds, aziridine compounds, blocked isocyanate compounds; inorganic compounds such as ammonium persulfate, ferric chloride, magnesium chloride, sodium tetraborate, potassium tetraborate; boric acid, trysterol borate, boron-based polymers, hydrazide compounds, glyoxylates, etc. These may be used individually or in combination of two or more. The amount of crosslinking agent used is preferably in the range of 0.1 to 10 parts by mass, and more preferably in the range of 1 to 10 parts by mass, per 100 parts by mass of the total solid content of the thermal recording layer. This can improve the water resistance of the thermal recording layer.

[0033] (Waxes) Examples of waxes include paraffin wax, carnauba wax, microcrystalline wax, polyolefin wax, polyethylene wax, and other waxes; for example, higher fatty acid amides such as stearic acid amide and ethylenebisstearic acid amide, higher fatty acid esters, and their derivatives.

[0034] (Metallic soaps) Examples of metallic soaps include polyvalent metal salts of higher fatty acids, such as zinc stearate, aluminum stearate, calcium stearate, and zinc oleate. Furthermore, if necessary, various auxiliary agents such as oil repellents, defoamers, and viscosity modifiers can be added to the thermal recording layer, to the extent that they do not impair the effects of the present invention.

[0035] The heat-sensitive recording layer is produced, for example, as follows: using water as a dispersion medium, a leuco dye and a developer, each optionally together with a sensitizer or a storage stability improver or separately, are dispersed together with a water-soluble synthetic polymer compound such as polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, methyl cellulose, a styrene-maleic anhydride copolymer salt, and other surfactants by various stirring / wet pulverizers such as a ball mill, a co-ball mill, an attritor, vertical and horizontal sand mills, to prepare respective dispersions, then the dispersions obtained by micronization to an average particle diameter of 2 μm or less are used, an adhesive is mixed, and auxiliaries are mixed as needed to prepare a coating for a heat-sensitive recording layer, which is then applied and dried to form the heat-sensitive recording layer on a support. The coating amount of the heat-sensitive recording layer is not particularly limited, and the coating amount after drying is 1 to 12 g / m ２ is preferably about 2 to 10 g / m ２ is more preferably 2.5 to 8 g / m ２ is still more preferably 3 to 5.5 g / m ２ is particularly preferred. The heat-sensitive recording layer may be formed by being divided into two or more layers as needed, and the composition and coating amount of each layer may be the same or different.

[0036] [Protective Layer] In the heat-sensitive recording material, a protective layer may be optionally provided on the heat-sensitive recording layer. The protective layer preferably contains a pigment and an adhesive. Furthermore, for the purpose of preventing sticking to a thermal head, the protective layer preferably contains a lubricant such as an alkyl phosphate ester salt, an N-substituted fatty acid amide, or a stearate, and may also contain an ultraviolet absorber. In addition, providing a glossy protective layer can increase the added value of the product.

[0037] The pigment contained in the protective layer is not particularly limited, and examples thereof include inorganic pigments such as amorphous silica, kaolin, clay, light calcium carbonate, heavy calcium carbonate, calcined kaolin, titanium oxide, magnesium carbonate, aluminum hydroxide, colloidal silica, and synthetic layered mica, and plastic pigments such as urea-formalin resin filler.

[0038] The adhesive contained in the protective layer is not particularly limited, and a water-soluble or water-dispersible aqueous adhesive can be used. The adhesive can be appropriately selected from those that can be used in the heat-sensitive recording layer. Among these adhesives, various modified polyvinyl alcohols such as acetoacetyl-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and diacetone-modified polyvinyl alcohol are more preferably used.

[0039] An alkyl phosphate ester salt is a compound in which a hydrogen atom in at least one of the three hydroxy groups of phosphoric acid is substituted with an alkyl group, and among these, a monoester form (monoalkyl phosphate ester) is preferable. The number of carbon atoms in the alkyl group of the ester moiety in the alkyl phosphate ester is preferably 12 to 36, more preferably 12 to 30, and still more preferably 14 to 22. The alkyl group may be linear or branched. Examples of the alkyl phosphate ester salt include inorganic salts, organic amine salts, basic amino acid salts, and the like. Examples of the inorganic salt include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as magnesium salts and calcium salts; ammonium salts; aluminum salts; zinc salts and the like. Examples of the organic amine salts include monoethanolamine salts, diethanolamine salts, triethanolamine salts, and the like. Examples of the basic amino acid salts include arginine salts, lysine salts, and the like.

[0040] Specific examples of N-substituted fatty acid amides include N,N'-ethylene bislauric acid amide, N,N'-methylene bisstearic acid amide, N,N'-ethylene bisstearic acid amide, N,N'-ethylene bisoleic acid amide, N,N'-ethylene behenic acid amide, N,N'-ethylene bis-12-hydroxystearic acid amide, N,N'-butylene bisstearic acid amide, N,N'-hexamethylene bisstearic acid amide, N,N'-hexamethylene bisoleic acid amide, N,N'-xylylene bisstearic acid amide, stearic acid monomethylol amide, N,N'-dioleyl adipic acid amide, N,N'-distearyl adipic acid amide, N,N'-distearyl sebacic acid amide, N,N'-distearyl terephthalic acid amide, N,N'-distearyl isophthalic acid amide, and the like.

[0041] Specific examples of stearates include zinc stearate, lithium stearate, magnesium stearate, aluminum stearate, calcium stearate, strontium stearate, barium stearate, cadmium stearate, lead stearate, and the like, with zinc stearate being preferable.

[0042] The protective layer is formed on the heat-sensitive recording layer, for example, by applying a protective layer coating prepared by using water as a dispersion medium and mixing a pigment, an adhesive, and optionally an auxiliary agent or the like, followed by drying. The coating amount of the protective layer coating is not particularly limited, and is 0.3 to 15 g / m in terms of dry mass ２ is preferable, and 0.3 to 10 g / m ２ is more preferable, 0.5 to 8 g / m ２ is still more preferable, 1 to 8 g / m ２ is particularly preferable, and 1 to 5 g / m ２ is even more preferable. The protective layer may be formed by being divided into two or more layers as necessary, and the composition and coating amount of each layer may be the same or different.

[0043] [Undercoat layer] The thermal recording material of the present invention may optionally include an undercoat layer between the support and the thermal recording layer. The undercoat layer preferably contains an adhesive, and more preferably contains hollow particles.

[0044] (Adhesives) Examples of adhesives include water-soluble polymer materials such as polyvinyl alcohol and its derivatives, starch and its derivatives, cellulose derivatives such as hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose, carboxymethylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide-acrylic acid ester copolymer, acrylamide-acrylic acid ester-methacrylic acid ester copolymer, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, casein, gelatin and their derivatives, as well as emulsions such as polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid ester, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, and ethylene-vinyl acetate copolymer, or water-insoluble polymer latex such as styrene-butadiene copolymer and styrene-butadiene-acrylic copolymer. These can be preferably used on polyester films such as PET film and polyester resin laminated paper. Among these, it is preferable to use an adhesive containing latex. Examples of aqueous adhesives or solvent-based adhesives include chlorinated polyolefin resins. Chlorinated polyolefin resins can be preferably used with polyolefin films such as PP films, polyolefin synthetic paper, polyolefin resin laminated paper, paper such as glassine paper, and supports such as cellophane. The adhesive content can be selected from a wide range, but generally it is preferably about 10 to 70% by mass, and more preferably about 15 to 60% by mass, of the total solid content of the undercoat layer.

[0045] The adhesive preferably contains a binder resin with a glass transition temperature (Tg) of -10°C or lower. A glass transition temperature of -10°C or lower allows for improved image quality even in the low-energy range. A glass transition temperature of -30°C or lower is more preferable, as it further improves image quality in the low-energy range. On the other hand, a temperature of -40°C or higher is preferable because stickiness occurs below -50°C, which is undesirable.

[0046] (Hollow Particles) Hollow particles made of organic resin can enhance the thermal insulation properties of the undercoat layer when incorporated into it. An undercoat layer with high thermal insulation properties can prevent the diffusion of heat applied to the thermal recording layer, thereby improving the sensitivity of the thermal recording medium.

[0047] Hollow particles made from organic resins can be classified into foamed and non-foamed types depending on the manufacturing method. Of these two types, foamed hollow particles have properties suitable for improving the heat insulation of the undercoat layer.

[0048] <Method for Manufacturing Hollow Particles> The following describes a typical method for manufacturing foamed hollow particles.

[0049] First, particles are created by encapsulating a volatile liquid inside a resin. By heating the resin, the resin is softened, and the liquid inside the particles is vaporized and expanded, thereby producing hollow particles.

[0050] During the manufacturing process, the internal liquid is heated and expanded, resulting in a larger hollow ratio in foamed hollow particles. This large hollow ratio provides high thermal insulation, allowing foamed hollow particles to enhance the sensitivity of thermal paper and improve recording density. Improved sensitivity is particularly important when developing colors in the mid-tone region, where less thermal energy is applied to the thermal recording layer. Furthermore, forming the thermal recording layer via a highly insulating undercoat prevents heat diffusion, thus preventing image blurring and improving image quality.

[0051] Resins that can be used for foamed hollow particles include thermoplastic resins such as styrene-acrylic resin, polystyrene resin, acrylic resin, polyethylene resin, polypropylene resin, polyacetal resin, chlorinated polyether resin, polyvinyl chloride resin, polyvinylidene chloride resin, acrylic resin (for example, acrylic resin containing acrylonitrile as a component), styrene resin, vinylidene chloride resin, and copolymer resins mainly composed of polyvinylidene chloride and acrylonitrile. Common gases contained inside foamed hollow particles include propane, butane, isobutane, and air. Among the various resins listed above, acrylonitrile resin and copolymer resins mainly composed of polyvinylidene chloride and acrylonitrile are preferred for use in hollow particles from the viewpoint of strength to maintain the shape of the foamed particles.

[0052] <Maximum Particle Diameter> The maximum particle diameter of the hollow particles is preferably 10 to 30 μm, more preferably 10 to 25 μm, and even more preferably 10 to 20 μm. The maximum particle diameter is also referred to as D100. When the maximum particle diameter of the hollow particles is 10 μm or more, the cushioning properties of the undercoat layer are improved, which improves the adhesion of the thermal paper to the thermal head during printing, resulting in a high-quality thermal recorder. A thermal recorder with such high adhesion to the thermal head can improve the recording density in the midtone region, where color is produced at an energy lower than the energy of the maximum recording density (Dmax). On the other hand, when the maximum particle diameter of the hollow particles is 30 μm or less, the smoothness of the undercoat layer is improved, which allows for the uniformization of the thermal recording layer provided via the undercoat layer, resulting in a thermal recorder with high color density. Furthermore, the adhesion between the support and the undercoat layer is improved, resulting in a thermal recorder with excellent strength of the coated surface. The maximum particle diameter of the hollow particles can be measured using a laser diffraction particle size distribution analyzer. Furthermore, it is also possible to perform measurements using an electron microscope.

[0053] <Median Diameter> When a powder is divided into two parts based on a certain particle size, the median diameter is the diameter at which the larger particles and the smaller particles occupy equal volumes, i.e., the particle diameter at which the 50% volume frequency occurs. The median diameter is also referred to as D50. The median diameter of hollow particles can be measured using a laser diffraction particle size distribution analyzer. It is also possible to measure it using an electron microscope. The median diameter of hollow particles is preferably 4.0 to 15 μm, and more preferably 7.5 to 15 μm. By setting the median diameter to 4.0 μm or more, cushioning properties can be improved. On the other hand, by setting it to 15 μm or less, smoothness can be improved.

[0054] <Ratio of Maximum Particle Diameter to Median Diameter> The ratio of the maximum particle diameter (D100) to the median diameter (D50) (D100 / D50) is an indicator of the degree of particle size distribution. D100 / D50 is preferably 1.8 to 3.0, more preferably 1.8 to 2.8, and even more preferably 1.8 to 2.6. By setting D100 / D50 to 1.8 or higher, the hollow particles foam sufficiently, the maximum particle diameter becomes sufficiently large, the hollowness ratio increases, and the heat insulation of the undercoat layer can be improved. On the other hand, by setting D100 / D50 to 3.0 or lower, the size of the hollow particles becomes uniform, the smoothness of the undercoat layer is improved, white spots in the image can be suppressed, and the recording density can also be improved.

[0055] <Hollow particles with a particle diameter of 2 μm or less> In the particle size distribution determined by a laser diffraction particle size distribution analyzer, it is preferable that the volume percentage of hollow particles with a particle diameter of 2.0 μm or less is 1% or less. Furthermore, it is more preferable that the volume percentage of hollow particles with a particle diameter of 2.0 μm or less is 0.5% or less, and even more preferable that they are not present at all. Hollow particles with a particle diameter of 2 μm or less are considered to have an extremely small contribution to heat insulation because their particle diameter is too small to provide a sufficient hollow region. By setting the volume percentage of hollow particles with a particle diameter of 2 μm or less in the undercoat layer to 1% or less, the recording density, image quality, etc. can be improved.

[0056] <Content> Hollow particles are preferably contained in an amount of 5 to 40% by mass of the total solid content of the undercoat layer, and more preferably in an amount of 5 to 30% by mass. When the content of hollow particles is 5% by mass or more, the heat insulation properties of the undercoat layer can be improved. On the other hand, when the content of hollow particles is 30% by mass or less, problems in terms of the strength of the coated surface are less likely to occur.

[0057] <Hollow Ratio> The hollow ratio of hollow particles is preferably 80-98%, more preferably 90-98%, and even more preferably 91-98%. When the hollow ratio of hollow particles is 80% or more, high heat insulation can be imparted to the undercoat layer containing the hollow particles, and image quality can also be improved. On the other hand, when the hollow ratio of hollow particles is 98% or less, the strength of the film surrounding the hollow part can be improved, making it possible to create hollow particles that do not collapse when the undercoat layer is formed.

[0058] The undercoat layer may contain at least one oil-absorbing pigment and thermally expandable particles, with an oil absorption capacity of 70 ml / 100 g or more, particularly 80 to 150 ml / 100 g. Here, the above oil absorption capacity is determined according to the method of JIS K 5101.

[0059] Various oil-absorbing pigments can be used, but specific examples include inorganic pigments such as calcined kaolin, amorphous silica, light calcium carbonate, and talc. The average particle size of the primary particles of these oil-absorbing pigments is preferably about 0.01 to 5 μm, and particularly preferably about 0.02 to 3 μm. The amount of oil-absorbing pigment used can be selected from a wide range, but generally it is preferably about 20 to 80% by mass, and more preferably about 25 to 75% by mass, of the total solid content of the undercoat layer.

[0060] The undercoat layer is formed on the support by applying an undercoat coating solution, prepared by mixing an adhesive, hollow particles, pigments, auxiliary agents, etc., with water as a medium, and then drying it. The amount of undercoat coating solution applied is not particularly limited, but is 2 to 20 g / m² by dry mass. ２ A suitable degree is 2-12 g / m ２ A more moderate degree is preferable.

[0061] Examples of additives contained in the primer coating liquid include dispersants such as sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, and fatty acid metal salts; waxes such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, and ester waxes; water-resistant agents such as hydrazide compounds, boric acid, dialdehyde starch, glyoxylates, and epoxy compounds; defoamers; coloring dyes; and fluorescent dyes.

[0062] [Other Layers] In this invention, an adhesive layer may be provided on at least one side of the support. This can increase the added value of the thermal recording material. As the adhesive layer, for example, by applying an adhesive, re-wettable adhesive, delayed-tack type adhesive, etc. to one side, adhesive paper, re-wettable adhesive paper, delayed-tack paper, etc. can be made. Alternatively, the side of the support opposite to the thermal recording layer can be used to provide functions such as thermal transfer paper, inkjet recording paper, carbonless paper, electrostatic recording paper, or zeography paper, thereby creating recording paper that can record on both sides. Of course, a double-sided thermal recording material can also be made. Furthermore, a back layer can be provided to suppress the penetration of oil and plasticizer from the back surface of the thermal recording material, to control curling, or to prevent static electricity. It is also possible to create a linerless label that does not require release paper by applying a release layer containing silicone on the protective layer and applying an adhesive to one side.

[0063] [Thermal Recording Material] A thermal recording material can be manufactured by forming the above layers on a support. Any known coating method can be used to form the above layers on the support, such as gravure printing, air knife method, blade method, gravure method, roll coater method, spray method, dip method, bar method, curtain method, slot die method, slide die method, or extrusion method. In addition, each coating may be applied or printed one layer at a time and dried as necessary to form each layer, or the same coating may be applied or printed in two or more layers. Furthermore, simultaneous multilayer coating may be performed in which two or more layers are applied at the same time. In addition, after each layer has been formed, or at any stage after all layers have been formed, a smoothing process can be performed using a known method such as a supercalender or softcalender.

[0064] The method for recording an image on the thermal recording medium of the present invention is not particularly limited and can be appropriately selected depending on the purpose. Examples of image recording methods include a thermal head printer and laser light (e.g., carbon dioxide laser, UV laser, semiconductor laser light, YAG laser light, fiber laser light, solid-state laser light, dye laser light, etc.). The wavelength of the laser light used is not particularly limited and can be appropriately selected depending on the purpose.

[0065] The present invention will be described in more detail by reference to examples, but the present invention is not limited thereto. Unless otherwise specified, "parts" and "%" refer to "parts by mass" and "% by mass," respectively.

[0066] (1) Preparation of leuco dye dispersion (Solution A) 40 parts of 3-di-(n-butyl)amino-6-methyl-7-anilinofluorane, 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and 20 parts of water were mixed and ground using a sand mill (AIMEX, sand grinder) until the median diameter measured by a laser diffraction particle size analyzer SALD2200 (Shimadzu Corporation) was 0.5 μm to obtain leuco dye dispersion (Solution A).

[0067] (2) Preparation of color developer dispersion (Solution B) 40 parts of 1,3-diphenylurea, 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and 20 parts of water were mixed and ground using a sand mill (manufactured by AIMEX, sand grinder) until the median diameter measured by a laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation) was 1.0 μm to obtain the color developer dispersion (Solution B).

[0068] (3) Preparation of color developer dispersion (Solution C) 40 parts of 5-(N-3-methylphenyl-sulfonilamide)-(N',N''-bis-(3-methylphenyl)-isophthalic acid diamide), 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and 20 parts of water were mixed and ground using a sand mill (AIMEX, sand grinder) until the median diameter measured by a laser diffraction particle size analyzer SALD2200 (Shimadzu Corporation) was 1.0 μm to obtain the color developer dispersion (Solution C).

[0069] (4) Preparation of color developer dispersion (Solution D) 40 parts of N-[2-(3-phenylureido)phenyl]benzenesulfonamide, 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and 20 parts of water were mixed and ground using a sand mill (AIMEX, sand grinder) until the median diameter measured by a laser diffraction particle size analyzer SALD2200 (Shimadzu Corporation) was 1.0 μm to obtain the color developer dispersion (Solution D).

[0070] (5) Preparation of color developer dispersion (Solution E) 40 parts of 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and 20 parts of water were mixed and ground using a sand mill (AIMEX, sand grinder) until the median diameter measured by a laser diffraction particle size analyzer SALD2200 (Shimadzu Corporation) was 1.0 μm to obtain the color developer dispersion (Solution E).

[0071] (6) Preparation of color developer dispersion (Solution F) 40 parts of N,N'-di[3-(p-toluenesulfonyloxy)phenyl]urea, 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and 20 parts of water were mixed and ground using a sand mill (AIMEX, sand grinder) until the median diameter measured by a laser diffraction particle size analyzer SALD2200 (Shimadzu Corporation) was 1.0 μm to obtain the color developer dispersion (Solution F).

[0072] (7) Preparation of color developer dispersion (Solution G) 40 parts of 4,4'-diaminodiphenyl sulfone, 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and 20 parts of water were mixed and ground using a sand mill (AIMEX, sand grinder) until the median diameter measured by a laser diffraction particle size analyzer SALD2200 (Shimadzu Corporation) was 1.0 μm to obtain the color developer dispersion (Solution G).

[0073] (8) Preparation of color developer dispersion (Solution H) 40 parts of 4,4'-dihydroxydiphenyl sulfone, 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and 20 parts of water were mixed and ground using a sand mill (manufactured by AIMEX, sand grinder) until the median diameter measured by a laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation) was 1.0 μm to obtain the color developer dispersion (Solution H).

[0074] (9) Preparation of sensitizer dispersion (Solution I) 40 parts of diphenyl sulfone, 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and 20 parts of water were mixed and ground using a sand mill (AIMEX, sand grinder) until the median diameter measured by a laser diffraction particle size analyzer SALD2200 (Shimadzu Corporation) was 1.0 μm to obtain the sensitizer dispersion (Solution I).

[0075] (10) Preparation of sensitizer dispersion (Solution J) 40 parts of 1,2-diphenoxyethane, 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and 20 parts of water were mixed and ground using a sand mill (AIMEX, sand grinder) until the median diameter measured by a laser diffraction particle size analyzer SALD2200 (Shimadzu Corporation) was 1.0 μm to obtain the sensitizer dispersion (Solution J).

[0076] (11) Preparation of sensitizer dispersion (Solution K) 40 parts of 1,2-di(3-methylphenoxy)ethane, 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and 20 parts of water were mixed and ground using a sand mill (AIMEX, sand grinder) until the median diameter measured by a laser diffraction particle size analyzer SALD2200 (Shimadzu Corporation) was 1.0 μm to obtain the sensitizer dispersion (Solution K).

[0077] (12) Preparation of Pigment Dispersion (Solution L) 100 parts of calcined kaolin, 0.8 parts of a dispersant (product name: Aron T-50, manufactured by Toagosei Co., Ltd., solid content concentration 40%), and 127 parts of water were mixed and stirred to obtain a pigment dispersion (Solution L).

[0078] (Example 1) (13) Preparation of primer coating liquid 56.6 parts of hollow particles (product name: Lowpake SN-1055, manufactured by Dow, median diameter (D50) 1.0 μm, maximum particle diameter (D100) 1.8 μm, hollowness 55%, solid content concentration 26.5%), 20.8 parts of styrene butadiene latex (product name: L-1571, manufactured by Asahi Kasei Corporation, solid content concentration 48%), 16 parts of a 25% solution of oxidized starch (product name: Petrocoat C-8, manufactured by Nippon Denki Chemical Co., Ltd.), 1.1 parts of carboxymethylcellulose (product name: SG AG Gum, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., solid content concentration 95%), 70 parts of L solution, and 100 parts of water were mixed and stirred to obtain a primer coating liquid.

[0079] (14) Preparation of coating solution for thermal recording layer 22.7 parts of solution A, 31.8 parts of solution B, 13.6 parts of solution C, 38.6 parts of solution I, 30 parts of pigment (product name: NipSeal E-743, manufactured by Tosoh Silica Co., Ltd.), 100 parts of a 10% aqueous solution of polyvinyl alcohol (product name: JF-05, manufactured by Nippon Vinegar & Polyvinyl Alcohol Co., Ltd.), 10 parts of a 10% aqueous solution of sodium dioctyl sulfosuccinate (product name: Sanmorin OT-70, manufactured by Sanyo Chemical Industries, Ltd.), 20.8 parts of zinc stearate (product name: Hydrin Z-9-36, manufactured by Chukyo Oil & Fat Co., Ltd., solid content concentration 36%), and 100 parts of water were mixed and stirred to obtain a coating solution for thermal recording layer.

[0080] (15) Preparation of thermal recording material Basis weight 60 g / m ２ On one side of the high-quality paper, the above-mentioned undercoat coating liquid and thermal recording layer coating liquid were applied in amounts of 6.0 g / m² each after drying. ２ 3.3 g / m ２ The material was coated and dried in such a manner to sequentially form a base coat layer and a thermal recording layer, and then the surface was smoothed with a supercalender to obtain a thermal recording body.

[0081] (Example 2) A thermal recording body was obtained in the same manner as in Example 1, except that the amount of liquid B was changed from 31.8 parts to 13.6 parts, and the amount of liquid C was changed from 13.6 parts to 31.8 parts.

[0082] (Example 3) In the preparation of the coating solution for the thermal recording layer in Example 2, the amount of solution C was changed from 31.8 parts to 4.5 parts, and 27.3 parts of solution D were added, except that a thermal recording body was obtained in the same manner as in Example 2.

[0083] (Example 4) In the preparation of the coating solution for the thermal recording layer in Example 2, the amount of solution C was changed from 31.8 parts to 4.5 parts, and 27.3 parts of solution E were added, except that a thermal recording body was obtained in the same manner as in Example 2.

[0084] (Example 5) In the preparation of the coating solution for the thermal recording layer in Example 2, the amount of solution C was changed from 31.8 parts to 4.5 parts, and 27.3 parts of solution F were added, except that a thermal recording body was obtained in the same manner as in Example 2.

[0085] (Example 6) In the preparation of the coating solution for the thermal recording layer in Example 3, the amount of solution C was changed from 4.5 parts to 2.3 parts, and 2.3 parts of solution E were added, except that a thermal recording body was obtained in the same manner as in Example 3.

[0086] (Example 7) A thermal recording body was obtained in the same manner as in Example 6, except that in the preparation of the coating solution for the thermal recording layer in Example 6, 2.3 parts of liquid F were used instead of 2.3 parts of liquid E.

[0087] (Example 8) A thermal recording body was obtained in the same manner as in Example 6, except that in the preparation of the coating solution for the thermal recording layer in Example 6, 2.3 parts of liquid G were used instead of 2.3 parts of liquid E.

[0088] (Example 9) A thermal recording body was obtained in the same manner as in Example 3, except that in the preparation of the coating solution for the thermal recording layer in Example 3, 38.6 parts of solution J were used instead of 38.6 parts of solution I.

[0089] (Example 10) A thermal recording body was obtained in the same manner as in Example 3, except that in the preparation of the coating solution for the thermal recording layer in Example 3, 38.6 parts of solution K were used instead of 38.6 parts of solution I.

[0090] (Comparative Example 1) A thermal recording body was obtained in the same manner as in Example 1, except that the amount of liquid B was changed from 31.8 parts to 45.4 parts and the amount of liquid C was changed from 13.6 parts to 0 parts.

[0091] (Comparative Example 2) A thermal recording body was obtained in the same manner as in Example 1, except that the amount of liquid B was changed from 31.8 parts to 0 parts, and the amount of liquid C was changed from 13.6 parts to 45.4 parts.

[0092] (Comparative Example 3) A thermal recording body was obtained in the same manner as in Example 1, except that in the preparation of the coating solution for the thermal recording layer in Example 1, 45.4 parts of liquid G were used instead of 31.8 parts of liquid B and 13.6 parts of liquid C.

[0093] The above examples and comparative examples were evaluated using the following method. The results are shown in Table 1.

[0094] [Color Density] Using a thermal recording evaluation machine (product name: Atlantek 400 from Printrex, Inc. (USA)), each thermal recording material was recorded with applied energy of 10.3 mJ / dot (mid-tone) and 16.0 mJ / dot (high-gradation). The optical density of the printed area of ​​each colored thermal recording material sample was measured using a spectrophotometer (X-rite eXact, manufactured by X-rite Inc.). The evaluation criteria were as follows: (Mid-tone) Optical density 1.00 or higher: A Excellent optical density 0.80 to 0.99: B Slightly low but usable optical density ~0.79: C Problems in practical use (High-gradation) Optical density 1.20 or higher: A Excellent optical density 1.10 to 1.19: B Slightly low but usable optical density ~1.09: C Problems in practical use

[0095] [Water Resistance] Using a thermal recording evaluation machine (product name: Atlantek 400 from Printrex Corporation (USA)), each thermal recording material was recorded with an applied energy of 10.3 mJ / dot. After each thermal recording material developed color, it was immersed in room temperature water (20°C) for 24 hours. The optical density of the printed area after treatment was measured using a spectrophotometer (X-rite eXact, manufactured by X-rite Corporation). The print retention rate was calculated using the following formula: Print retention rate (%) = (Optical density after treatment) / (Optical density before treatment) x 100. The evaluation criteria were as follows: (Water Resistance) Print retention rate 70% or more: A Usable Print retention rate ~69%: C Problems in practical use

[0096]

Claims

1. A thermal recording body having a thermal recording layer on a support containing at least a leuco dye, a color developer, and a sensitizer, characterized in that the thermal recording layer contains 1,3-diphenylurea and 5-(N-3-methylphenyl-sulfonamide)-(N',N''-bis-(3-methylphenyl)-isophthalic acid diamide as color developers.

2. The thermal recording body according to claim 1, wherein the thermal recording layer further contains at least one color developer selected from the group consisting of N-[2-(3-phenylureido)phenyl]benzenesulfonamide, 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, N,N'-di[3-(p-toluenesulfonyloxy)phenyl]urea, and diaminodiphenylsulfone.

3. The thermal recording body according to claim 1 or 2, wherein 5-(N-3-methylphenyl-sulfonilamide)-(N',N''-bis-(3-methylphenyl)-isophthalic acid diamide) is contained in 5 to 300 parts by mass per 100 parts by mass of 1,3-diphenylurea.

4. The thermal recording body according to claim 2, wherein N-[2-(3-phenylureido)phenyl]benzenesulfonamide is contained in 10 to 300 parts by mass per 100 parts by mass of 1,3-diphenylurea.

5. The thermal recording body according to claim 1 or 2, wherein the thermal recording layer contains at least one selected from the group consisting of diphenylsulfone, 1,2-diphenoxyethane, and 1,2-di(3-methylphenoxy)ethane as a sensitizer.

6. The thermal recording body according to claim 1 or 2, wherein a primer layer is provided between the support and the thermal recording layer, the primer layer contains hollow particles and an adhesive, the hollow particles have a maximum particle diameter (D100) of 10 to 30 μm, a particle diameter (D50) at a 50% volume percent frequency of the hollow particles of 4.0 to 15 μm, a ratio D100 / D50 of the maximum particle diameter (D100) to the particle diameter (D50) at a 50% volume percent frequency of the hollow particles of 10 to 3.0, and the volume percent of the hollow particles with a particle diameter of 2.0 μm or less is 1% or less.

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